This invention relates to a watch outer case polishing apparatus for automating a watch outer case polishing process by using a manipulator, and a watch outer case polishing apparatus and a general purpose polishing apparatus which arithmetically control the position and attitude of a workpiece and the force and moment exerted on a polishing wheel thereby in a functionally separated manner and simultaneously, and particularly to a watch outer case polishing apparatus and a general purpose polishing apparatus which can carry out stable control by attaining manipulator control equilibrium quickly and with which computation of position and other variables is simple and inexpensive.
Conventionally, the process of polishing a watch outer case has been carried out by hand by a skilled worker and has not been automated.
The polishing process can be roughly divided into coarse polishing, intermediate polishing and finishing polishing.
The construction of a coarse polishing apparatus conventionally used for polishing a watch outer case is shown in FIG. 15. In FIG. 15, the rotation shaft 2 of a polishing wheel 1 is supported in a predetermined spacial position. A plate 4 for a watch outer case 3 to be placed on is disposed with a small gap between it and the polishing wheel 1. The plate 4 is supported on a fixed base 7 by a plate arm 6 having screws 5a, 5b at its ends for changing the set position and attitude (angle) of the plate 4.
Using this arrangement, a worker carries out polishing in the following way:
The worker first places a watch outer case 3 on the plate 4. Then, with the underside of the watch outer case 3 in contact with the upper surface of the plate 4, the watch outer case 3 is slid toward the polishing wheel 1 and brought into contact with the polishing wheel 1. With the contact between the underside of the watch outer case 3 and the upper surface of the plate 4 still being maintained after the watch outer case 3 is brought into contact with the polishing wheel 1, the area of the watch outer case 3 making contact with the polishing wheel 1 is progressively changed as polishing is carried out. At this time, when polishing a watch outer case 3, it is necessary to polish the curved surfaces of the watch outer case 3 three-dimensionally. To do this, the worker adjusts the angle of the plate 4 to suit the surface being polished each time the surface being polished changes.
Because the operation must be performed by a skilled worker, the cost of a conventional, manual polishing operation has been high. Also, in recent years, the adoption of high-variety, low-quantity production has been progressing in the watch industry, and there has been the risk that even if a fixed sequence automatic polishing machine were to be developed it would not be flexible enough to cope with the demands of this kind of production.
Therefore, to solve the problems mentioned above, there has been a need to introduce a manipulator for realizing automation in the field of watch outer case polishing.
However, most manipulators which have been used for polishing in other fields hold the polishing wheel rather than the work and therefore are not suitable for introduction unchanged into the field of watch outer case polishing. Using such a manipulator for watch outer case polishing involves problems such as, since the polishing wheel is large and heavy, it is dynamically and controlwise, difficult to move. Because of this, also from the point of view of energy saving, the development of a manipulator which holds the watch outer case has been desired.
Also, even in the case of a manipulator which holds the work, with the kind of control which has conventionally been carried out there has been the following kind of problem: In FIGS. 16(a) to (d), a manipulator not shown in the drawings holds a piece of work 21. For example as shown in FIG. 16 (a), polishing is carried out by the work 21 being pressed against the polishing wheel 1 in the X direction with a force of 1 N! while the work 21 is moved in the Y direction as shown in FIG. 16(b). FIG. 16(c) shows a case wherein the above-mentioned control is continued unchanged even when there is a change in the polishing surface, and FIG. 16(d) shows a case wherein when there is a change in the polishing surface the attitude of the work 21 is changed and then the above-mentioned control is continued. From the viewpoint that force and position are controlled simultaneously the above-mentioned control is called hybrid control, but the control is completely divided into force control in the X direction and position control in the Y direction. Because of this, movement in the X direction is determined on the basis of force information only, and when there is a change in the polishing surface of the work 21 the X component of a detected force value for example falls and the manipulator tries to compensate this result and tends to cause vibration by overextending.
Furthermore, because hybrid control involves complicated matrix calculations, it is necessary to devise a mechanical construction suited to matrix calculation with which for example outside force estimation is easy.
Also, there is a need to be able to use a single manipulator with a plurality of polishing wheels 1 such as one for normal use and a spare or ones having different polishing grades.
Furthermore, to detect reaction forces at joint parts of the manipulator, force sensors and torque sensors or the like are provided for example in a wrist part of the manipulator, and there has been the problem that the proportion of the overall cost of the manipulator expended on such sensors is high.